Light emitting device including a plurality of LED chips and one mounting substrate has been proposed so far. (For example, references 1 and 2). The mounting substrate is formed of a circuit substrate, a sub-mount member, or the like, and arranged to hold the LED chip.
This light emitting device may suffer from short-circuit between the LED chips when adjacent LED chips are closely positioned, by way of an electrically conductive adhesive (e.g., Ag-epoxy resin and solder) and a patterned conductor which is formed at a portion of mounting LED chips on a dielectric substrate (e.g., AlN, Al2O3, FR5).
When adhesive is applied in small amount on the patterned conductor for overcoming this problem, this light emitting device may suffer from void-generation within bonding portion between the LED chip and the mounting substrate, so as to lose its bonding reliability and its heat-dissipation property.
The reference 1 discloses a light emitting device, in which the mounting substrate is provided with a through hole and a groove. The through hole and groove act to stock therein an extra adhesive, in the process of connecting the LED chip with the conductor pattern on the mounting substrate by means of the adhesive.
The light emitting device of reference 1 includes the mounting substrate which is made of a material having low solder-wettability such as a ceramic (e.g., AlN and Al2O3) and a glass epoxy resin (e.g., FR5). When the LED chip 110 is mounted on the patterned conductor 131 by way of solder bond in fabrication of this light emitting device, extra liquid solders overflowing from a bonding portion 115 may form solder balls 116, rather than flowing along an inner surface of the stock portion 134, as shown in FIG. 9. As a result, the light emitting device of reference 1 may suffer from short-circuit between adjacent LED chips 110 through bridging solder balls. When LED chip are mounted on a patterned conductor by way of solder in fabrication of the light emitting device of reference 2, extra liquid solders may overflow outside from the LED chip due to a force applied thereon, possibly causing short-circuit through extra solder as well as causing disposition of the LED chips.
Reference 1: Japanese unexamined patent publication 1996-88409 (paragraphs 0011 to 0017 and FIG. 1)
Reference 2: Japanese unexamined patent publication 2006-502567 (paragraph 0032 and FIGS. 3 and 4)